Colorectal Cancer:Diagnosis

Nearly all cases of colorectal cancer begin with the growth of polyps, or benign growths of tissue, in the intestine. If these growths are detected and removed early, the development of colorectal cancer can be prevented. Men and women over age 50 at average risk should be screened. Other family members of individuals with colorectal cancer should begin screening 10 years before their family member was diagnosed with a cancer, even if no genetic mutation was found.

A number of tests are available to screen for colorectal polyps or cancer. The following may be used alone or in combination:

  • Fecal Occult Blood Test (FOBT) — This test checks for occult (hidden) blood in the stool.
  • Flexible Sigmoidoscopy — In this examination, a doctor examines the inside of the rectum and lower portion of the colon through a flexible, lighted tube. The doctor may remove polyps and collect samples of tissue or cells for closer examination.
  • Colonoscopy — Colonoscopy is used to detect precancerous colon polyps before they become malignant. In this examination, a doctor looks at the inside of the rectum and entire colon through a flexible, lighted tube. The doctor may remove polyps and collect samples of tissue or cells for closer examination. 
  • Double Contrast Barium Enema — The patient is given an enema containing a dye barium), followed by an injection of air. X-rays of the rectum and colon are then taken. The barium outlines the intestine on the x-ray film, so that polyps and other abnormalities may be easily seen.
  • CT Colonography (“Virtual Colonoscopy”) –this is a non-invasive way to visualize the colon using a CT scanner. The main disadvantage is that if something abnormal is seen, the patient then needs a regular colonoscopy or sigmoidoscopy to obtain a biopsy or remove a polyp.Sigmoidoscopy allows examination of the lower third of the large bowel. About 65 percent of all precancerous polyps are found in this region. During colonoscopy, the entire colon is examined from the anus all the way to the junction of the small intestine and the colon.

Patients should speak with their physician about the screening method that is best for them.These examinations are important not only to determine the extent of the current problem, but also to look for other abnormalities, which might also be present and could influence your best course of treatment. The physician will determine which test is appropriate for each patient.

Additional tests are often required including

  • Blood tests CBC (complete blood count), blood chemistries and coagulation parameters. If the patient is anemic or there is risk of significant blood loss, a sample will be held at the blood bank if transfusion becomes necessary.
  • A CT scan or MRI of the abdomen may be ordered to determine whether or not the cancer has spread. These scans create a series of pictures of the colon from many angles. It can detect enlarged lymph nodes, which may signal more advanced cancer, infection, or a benign mass.
  • A Transrectal Ultrasound is often ordered to evaluate rectal cancer, determining the depth of a tumor and degree of lymph node involvement. This approach uses sound waves to take images of the bowel wall. A small, microphone-like instrument called a transducer is placed into the rectum. The transducer emits sound waves and picks up the echoes as they bounce off body tissues. These echoes then appear as a black and white image on a computer screen. This test is painless and does not expose the patient to radiation.